1. Field of the Invention
The present invention relates to a magnetoresistive effect element and a magnetic memory.
2. Related Art
Magnetoresistive effect elements using magnetic material films are used in, for example, magnetic heads and magnetic sensors. In addition, it is proposed to use the magnetoresistive effect elements in solid state MRAMs (Magnetic Random Access Memories).
As a magnetoresistive effect transistor element which has a sandwich structure film formed by inserting a single layer of a dielectric between two ferromagnetic layers, which lets a current flow perpendicularly to the film surface, and utilizes a tunnel current, the so-called “ferromagnetic TMR (Tunneling Magneto-Resistance effect) element” is proposed. Since it has become possible to obtain a magnetoresistance change rate of 20% or more in the ferromagnetic tunneling magneto-resistance effect element, technical development for commercial application of the element to the MRAM is being conducted vigorously.
This TMR element can be implemented by forming a thin Al (aluminum) layer having a thickness in the range of 0.6 nm to 2.0 nm on a ferromagnetic layer, exposing a surface of the Al layer to oxygen glow discharge or oxygen gas, and thereby forming a tunnel barrier layer.
A ferromagnetic single tunnel junction having a structure obtained by providing one of the ferromagnetic layers having the tunnel barrier layer of a ferromagnetic single tunnel junction between with an antiferromagnetic layer is proposed. Furthermore, a ferromagnetic tunnel junction having magnetic particles scattered in a dielectric, and a ferromagnetic double tunnel junction having a continuous film as each of the ferromagnetic layers.
These magnetoresistive effect elements also have a possibility of being applied to the MRAMs because it has become possible to obtain a magnetoresistance change rate in the range of 20% to 50% and the decrease of the magnetoresistance change rate can also be suppressed by raising the voltage value applied to the TMR element to obtain a desired output voltage value. If a TMR element is used as a memory element of an MRAM, one of ferromagnetic layers having a tunnel barrier layer between is used as a magnetization pinned layer and the other of the ferromagnetic layers is used as a magnetic recording layer. The memory element using the ferromagnetic single tunnel junction or the ferromagnetic double tunnel junction is non-volatile, and has a potential that a write and read time is 10 nanoseconds or less and the number of times of rewriting is also 1015 or more. Especially in the memory element using the ferromagnetic double tunnel junction, the decrease of the magnetoresistance change rate can be suppressed even if the voltage value applied to the TMR element is raised, as described above. Therefore, a large output voltage is obtained, and characteristics that are favorable for the memory element are obtained.
As regards the cell size of the memory, there is a problem that the size cannot be made smaller than a semiconductor DRAM (Dynamic Random Access Memory) or less in the case where an architecture in which a memory cell is formed of one transistor and one TMR element.
In order to solve this problem, a diode type architecture including a series connection composed of a TMR element and a diode between a bit line and a word line and a simple matrix type architecture obtained by arranging cells each having a TMR element between a bit line and a word line are proposed.
In either case, inversion is conducted using a current magnetic field based on a current pulse when writing to the magnetic recording layer is executed, resulting in high power consumption. When the capacity is increased, there is a limit in allowable current density for wiring and consequently a large capacity cannot be obtained. Unless the absolute value of the current is 1 mA or less, or it is 0.2 mA or less for substitution for DRAMs, the area of the driver increases. As compared with other non-volatile solid-state memories, such as ferroelectric random access memories using ferroelectric capacitors or flash memories, there is a problem that the chip becomes large and competitive power is lost.
In order to solve the above-described problem, a solid-state magnetic memory having a thin film formed of a high permeability magnetic material around writing wiring is proposed. According to these magnetic memories, a high permeability magnetic film is provided around wiring, and consequently a current value required to write information into the magnetic recording layer can be reduced efficiently.
Even if they are used, however, it is very difficult to cause the write current value to become 1 mA or less.
In order to solve these problems, a write method using a spin injection method is proposed (see, for example, U.S. Pat. No. 6,256,223). This spin injection method utilizes inversion of magnetization of the magnetic recording layer obtained by injecting a spin-polarized current into the magnetic recording layer of the memory element.
In the case where the spin injection method is applied to the TMR element, there is a problem of element destruction such as breakdown of a tunnel insulation film and there is a problem in element reliability.
Even if writing is conducted using the spin injection method, therefore, it is necessary to provide a new magnetoresistive effect element, and material, structure and architecture of a magnetic memory capable of decreasing the current density at the time of writing to the extent that element destruction is not caused.
As described heretofore, a new highly reliable magnetoresistive effect element, and material, structure and architecture of a magnetic memory which make possible operation with low power consumption and low current writing and without element destruction are needed.